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Session 49 - Young Stellar Objects.
Display session, Tuesday, January 14
Infrared companions to young stellar objects (YSOs) have been discovered in a number of sources. These companions are significantly redder than the "primary" component, but will often have a greater bolometric luminosity. Since one generally assumes that members of a binary system form at the same time, how is it that two objects separated by a projected distance of only a few hundred AU can have such strikingly different spectral energy distributions (SEDs)? In their review of infrared companions, Zinnecker amp; Wilking (1992, in Binaries as Tracers of Stellar Formation) offer three scenarios for the formation of such systems: 1) the members form coevally (within \sim 10^5 yr) but are of different masses, thus evolve at different rates; 2) the system is coeval, but the companion is viewed through the primary's circumstellar disk and thus suffers greater extinction; or 3) the members have similar evolutionary timescales but form at different times so that the younger component is still more deeply embedded.
We have observed several of these systems with JPL's mid-infrared camera MIRLIN from 5-25 microns, including narrowband images through the 10 micron silicate feature. Two are high mass systems (S255-IRS1 and GL961), three are low mass Class I YSOs (Haro 6-10, HH43-IRS1, and SSV63), and two are T Tau stars (DK Tau and UZ Tau). The four brighter systems (S255, GL961, Haro 6-10, and SSV63) were detected over the whole wavelength range; in each case we find that the silicate feature is deeper in the companion, implying a higher line of sight optical depth. For all sources, we combine this new data with available near-infrared information in an effort to derive accurate SEDs and luminosities for all members of these systems. Finally, we discuss the implications of our observations for the three scenarios above.
Program listing for Tuesday